SN instructed patient/ CG about Miralax to relieve constipation. SN instructed that MiraLax is used as a laxative to treat occasional constipation or irregular bowel movements. Common MiraLax side effects may include: bloating, gas, upset stomach; dizziness; or increased sweating.Get emergency medical help if you have any signs of an allergic reaction to MiraLax such as: hives; difficult breathing; swelling of your face, lips, tongue, or throat. Stop taking this medicine and call your doctor at once if you have: severe or bloody diarrhea; rectal bleeding; blood in your stools; or severe and worsening stomach pain.